Creating Functional Nanocrystal-Molecule Interfaces for Spin-triplet Energy Transfer

化学系的大分子、超分子和纳米化学项目支持德克萨斯大学奥斯汀分校的肖恩·T·罗伯茨教授研究材料中发生的光触发过程。光通过光合作用为植物生长提供能量，被用于无线通信的电子设备，甚至构成了非侵入性医疗的基础，例如用于治疗癌症的光动力疗法。然而，光以一种特殊的方式传输它的能量，通过被称为光子的粒子。不同颜色的光包含具有不同能量的光子，重要的是光子能量与其预期的应用相匹配。能量太低的光子无法完成预期的任务，而能量太大的光子会浪费能量，并会对部件造成损坏。这项研究项目开发了一种材料，通过将成对的光子组合成单个高能光子或将单个光子转换为多个低能量光子来重塑光的能量内容。一旦形成，这些材料可以作为能量传递剂，改善太阳能收集和量子计算。除了在研究项目上与学生密切合作外，罗伯茨教授还创立并参与了德克萨斯大学奥斯汀分校和奥斯汀社区学院之间的绿色能源(GREAT)项目。Great的目标是通过有针对性的指导和研究经验增加获得学位的社区大学生的数量。由有机染料分子化学功能化的半导体量子点为光子转换提供了理想的界面。被光吸收激发的量子点可以将它们的能量传递给它们表面的分子，促使它们进入自旋三重态激子状态。如果大量形成，自旋-三重态激子对可以经历三重态融合，这一过程将它们的能量结合在一起，形成一个可以辐射光的高能自旋-单重态。同样，光激发染料分子可以推动三重态融合的反向过程--单重态裂变，这会产生成对的三重态激子，每个激子都可以传递到量子点，以驱动红外光发射。这些方案需要一个关键的步骤，即通过量子点：分子界面传输自旋三重态激子，然而，对于这些界面的结构如何影响自旋三重态激子传输的速度和效率的理解是难以捉摸的。为了满足这一需求，德克萨斯大学奥斯汀分校的罗伯茨教授领导了一个团队，该团队使用受控化学合成、2D核磁共振和飞秒时间分辨光谱以及电子结构计算。该研究小组研究了量子点的化学结构：由PbS和Si两种互补量子点材料形成的分子界面如何影响自旋三重态激子转移。该项目致力于创造新的混合有机：用于光驱能源和燃料生产的无机结，以及用于量子计算和信息存储的利用自旋纠缠的材料。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division supports Professor Sean T. Roberts at the University of Texas at Austin to study light-triggered processes that occur in materials. Light provides the energy that fuels plant growth via photosynthesis, is used in electronics for wireless communication, and even forms the basis for noninvasive medical treatments, such as photodynamic therapy used to treat cancer. However, light transmits its energy in a peculiar manner, via particles known as photons. Different colors of light contain photons with different amounts of energy, and it is important that photon energies be matched to their intended applications. Photons with too little energy are unable to meet their intended task while photons with too much energy waste energy and can cause damage to components. This research project develops materials that reshape light’s energy content by combining pairs of photons into a single high-energy one or converting individual photons into multiple lower-energy photons. Once formed, these materials can serve as energy transfer agents improving solar energy harvesting and quantum computation. In addition to working with students closely on the research projects, Professor Roberts also founded and participates in the GReen Energy At Texas (GREAT) program, which was formed between the University of Texas at Austin and Austin Community College. GREAT aims to increase the number of community college student that earn degrees through targeted mentorship and research experiences.Semiconductor quantum dots chemically functionalized with organic dye molecules offer an ideal interface for photon conversion. Quantum dots energized by light absorption can pass their energy to molecules at their surface, promoting them into spin-triplet exciton states. If formed in high quantity, pairs of spin-triplet excitons can undergo triplet fusion, a process that combines their energy to form a single high-energy spin-singlet state that can radiate light. Likewise, photoexciting the dye molecules can fuel triplet fusion’s inverse process, singlet fission, which creates pairs of triplet excitons that can each pass to the quantum dot to drive infrared light emission. These schemes require a key step, the transfer of a spin-triplet exciton across the quantum dot:molecule interface, yet an understanding of how the structure of these interfaces impacts the rate and efficiency of spin-triplet exciton transfer is elusive. To address this need, Professor Roberts at the University of Texas at Austin directs a team that employs controlled chemical synthesis, 2D NMR and femtosecond time-resolved spectroscopies, and electronic structure calculations. The research team investigates how the chemical structure of quantum dot:molecule interfaces formed by two complementary quantum dot materials of PbS and Si impact spin-triplet exciton transfer. This project contributes to the creation of new hybrid organic:inorganic junctions for light-driven production of energy and fuels as well as materials that use spin entanglement for quantum computation and information storage.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.